This invention relates generally to a counterbalanced or counterpoised supporting arm, which is utilized to support a particular object on the free end of an arm and permit vertical adjustment of the supported object. The instant invention is extremely useful for supporting a dental x-ray unit which must provide some vertical position adjustment for extraoral movement relative to the patient but provide extreme stability once it is positioned for allowing the x-ray to be taken. Other uses could be stabilization of lamps, tables, television sets and the like which require adjustable, stabilized vertical positioning.
The prior art shows a plethora of counterbalanced support arms which have been complex in construction and operation. One such counterbalancing mechanism is shown in U.S. patent 2941776 issued to N. E. Lauterbach which shows an outer tubular support arm having a spring encased with a second tube, the device including fixed linkage arms attached to end supporting devices. One of the drawbacks of the Lauderbach device is the complexity of construction and spring tension adjustment. Many of the other devices shown in the prior art utilize cables and counter weights and elaborate spring counter weight systems to achieve the counterbalancing of the arm. Other drawbacks in the prior art devices include the limitations placed on the angular travel of the arm due to the particular type of mechanism employed.
With regard to overall supporting arm mechanisms especially in the dental field, many offices today have relatively low ceiling heights which make impractical devices shown in the prior art which in effect are jointed vertical support arms which in order to store vertically require high ceilings for storage. Utilizing the instant invention in conjunction with a plurality of rigid horizontally movable arms, a dental x-ray unit can be conveniently stored against the wall or the like and extended horizontally with the final vertical position being achieved by the counterbalancing mechanism of the instant invention.
The instant invention also provides for a readily lockable device which may lock the arm in a fixed position, a feature not shown in the prior art.